Hermetic refrigeration compressors (of small or medium size), such as those generally used in household refrigeration appliances, are also used in other refrigeration systems such as, for example, ice cube-making machines. In such systems, the periodic defrost of an evaporator of the refrigeration system is carried out by the refrigerant fluid itself in the form of heated gas, which leaves the discharge of the compressor.
In a refrigeration system (of small or medium size), return of liquid refrigerant in the suction system is common due to incomplete vaporization of the liquid refrigerant. In this case, if a liquid separating device is not provided in the refrigeration circuit, the compressor may be damaged. The most common causes for liquid return are: excess refrigerant load in the refrigeration system; inadequate refrigeration of the evaporator; and incorrect adjustment of the expansion device. The phenomenon of liquid return is more intense in commercial compressors of high capacity and low-evaporation temperature.
Some compressors (see FIGS. 1 and 1A) present an open suction, that is, a suction-inlet tube 1, disposed through a wall of a shell 2, is opened to the interior of the latter. With this construction, the refrigerant fluid—in the form of gas—which reaches the suction-inlet tube 1, is admitted in the interior of the hermetic shell 2 of the compressor and is drawn from the internal environment of the shell 2 to the interior of a suction muffler 3 and, thence, to the interior of the compression chamber of the compressor.
In these known compressors, the suction-acoustic muffler 3 is provided in the interior of the hermetic shell 2, spaced from and above the suction-inlet tube 1. This suction arrangement allows the refrigerant fluid—in the form of gas—to be heated during its permanence in the interior of the shell 2, due to its contact with hot components of the compressor, before being drawn to the interior of the suction muffler 3 and, subsequently, to the interior of the compression chamber. The heating of the refrigerant fluid in the interior of the shell 2 presents the inconvenience of reducing the volumetric pumping capacity and, consequently, the energetic efficiency of the compressor. An example of this construction is presented in JP2008-267365, in which the flow admitted in the interior of the shell 2, through the outlet nozzle 1a of the suction-inlet tube 1, is deflected by the head, before reaching the inlet nozzle 4 of the admission tube 5 of the suction muffler 3, which is positioned spaced from the outlet nozzle 1a of the suction-inlet tube 1.
There are also known direct-suction compressors (see FIG. 1B), in which the refrigerant fluid, in the form of gas, returning to the compressor by the suction-inlet tube 1, is integrally directed to the interior of the suction muffler 3, without being admitted in the interior of the hermetic shell 2. In this type of suction arrangement, the refrigerant fluid is drawn to the compression chamber, through the suction-inlet tube 1 and through the suction muffler 3, without being subjected to the hot components of the compressor of the open-suction arrangement and, thus, yields a higher energetic efficiency of the compressor.
However, a direct-suction arrangement (FIG. 1B) can only be used in applications in which there is no risk of the refrigerant fluid—in the liquid state—being admitted in the compression chamber of the compressor. Nevertheless, in certain refrigeration systems—such as those used in ice cube-making machines a defrost operation for removing ice that accumulates in the evaporator region should be periodically carried out by the operation of the compressor. In this type of defrost operation, an inversion is made in the circuit of the refrigerant fluid in the refrigeration system, so that the refrigerant gas compressed and heated by the compressor is directed to an inlet of the evaporator and not to an inlet of the condenser, as it would during normal operation of a conventional refrigeration cycle.
During the defrost operation—in which the refrigeration system is submitted to cycle inversion—the refrigerant fluid is at least partially condensed in the evaporator, passes to the liquid phase, and is returned to the compressor. The refrigeration system remains operating in the inverted cycle during a certain period of time, until the desired degree of defrost has been obtained. Once the degree of defrost is obtained, the refrigeration system operates in the conventional manner with the refrigerant fluid in the gas phase and compressed by the compressor—being directed to the condenser inlet.
The refrigerant fluid in the liquid phase that leaves the evaporator and returns to the compressor during the defrost operation, has to be diverted from the normal-suction path to prevent it from being compressed by the compressor cylinder and causing a high inner pressure and consequent damages to the valves, gaskets and other parts of the compressor. Therefore, it is not possible to use a direct suction in these applications.
In order to prevent the liquid refrigerant fluid from entering into the suction chamber, some compressor constructions (particularly those for commercial application and which may be subjected to return of liquid during operation) present the suction muffler 3 provided with a refrigerant fluid inlet nozzle 4 spaced from the outlet nozzle 1a of the suction-inlet tube 1, which outlet nozzle 1a is opened to the interior of the compressor shell 2.
In the solution presented in JP2005-133707, the suction-acoustic muffler presents a refrigerant-fluid-admission tube provided spaced from the inner end of the suction-inlet tube. The admission tube presents a refrigerant-fluid-inlet nozzle substantially aligned with the inner end of the suction-inlet tube and conformed to incorporate a deflector defined for better admission of gaseous refrigerant fluid received through the suction-inlet tube. Nevertheless, during the suction, the spacing between the inner end of the suction-inlet tube and the inlet nozzle of the admission tube of the suction-acoustic muffler is not sufficient to prevent oil or refrigerant fluid in the liquid phase from being further drawn to the interior of the compressor, thereby damaging the latter.
In many hermetic compressor constructions (see FIG. 1) to be used in ice cube-making machines or in other applications in which there is the risk of liquid-refrigerant fluid returning to the compression chamber, the suction-inlet tube 1 is provided spaced from the refrigerant-gas inlet nozzle 4 in the suction muffler 3, generally opposed to each other in the interior of the shell 2, according to the open suction arrangement. In this type of mounting arrangement although eliminating the risk of liquid-refrigerant fluid returning to the interior of the compression chamber the loss of energetic efficiency of the compressor is not avoided due to the heating of the refrigerant fluid, as the latter is admitted in the interior of the hermetic shell 2 before being drawn to the interior of the suction muffler 3 and, therefrom, to the interior of the compression chamber.
There are also known in the art some suction arrangements which aim at minimizing or suppressing the risk of liquid-refrigerant fluid (or even oil) returning to the suction muffler, without submitting the refrigerant fluid to an undesirable heating in the interior of the hermetic shell. Examples of these arrangements can be seen in patent JP2007-255245.
In the solution presented in JP2007-255245, the suction-inlet tube comprises an extension internal to the compressor shell and formed by a lower portion that is leveled with the suction-inlet tube for a temporary accumulation of the liquid-refrigerant fluid which by chance exists in the suction flow and by an upper portion that is elevated in relation to the suction-inlet tube to conduct only the gaseous-refrigerant fluid and having an outlet nozzle axially spaced in relation to the inlet nozzle of the suction muffler. The nozzle incorporates a deflector defined for better admission of the gaseous-refrigerant fluid received through the suction-inlet tube. It should be noted that the provision of the deflector is desirable due to the fact that the inlet nozzle of the suction muffler has its axis coplanar to the axis of the outlet nozzle of the upper portion of the inner extension of the suction-inlet tube, but forming with the latter an approximately right dihedral angle by reasons of space and to prevent any liquid refrigerant which reaches the upper portion of the inner extension from being supplied to the suction muffler.
In this previous solution, there is a semi-direct suction, according to which the liquid-refrigerant fluid which by chance reaches the liquid accumulator is stored therein until reaching a determined volume capable of activating a valve element—such as an articulated cover which opens under pressure of the accumulated liquid—that allows the liquid to be discharged in the interior of the shell, without being directed to the compression chamber.
Although the previous solution commented above minimizes or even impairs the admission of liquid-refrigerant fluid in the compression chamber of the compressor, it is complex and onerous to be carried out, requiring changes to be made in the construction of the suction-inlet tube, generally in the form of an additional piece having two distinct outlets.